Best practice when value selected

Hi,
I am using Phalcon\Tag::select to load the country list ..
I want when a country is selected from the select element , another select element which holds the city list will be loaded.
what is the best way to do it using phalcon ??

I believe I need to call an ajax function to load the other select elemnt , for example ajax function which call LoadCountries.php and than using TAG/Replace ,
or ther is a better way ?